The invention relates generally to electrical machines and, in particular, to a system and method of monitoring health of electrical machines.
Electrical machines such as power generators and motors typically include a rotating member (or rotor) and a stationary member (or stator). It is useful to monitor stator bar windings of the stator to ensure the windings are motionless during operation of the electrical machine. In some embodiments, an electrical machine includes a wedge system to induce a radial retaining force to a stator for reducing movement of the stator bar windings within slots of the stator. In a more specific embodiment, ripple springs are embedded in the stator winding assembly in a state of compression to keep the windings from moving. In such embodiments, if the wedge system becomes loose, the amount of retaining force is reduced such that the stator bar windings may move during operation. Over time, relative motion of the stator bar windings may cause damage to the insulation surrounding the stator bar wedges and a potential for a stator bar winding failure can occur. To prevent such a failure, the health of the electrical machine is periodically monitored to determine if any stator bar winding movement within the stator slots exceeds predetermined tolerances.
Currently, several methods and systems are used for monitoring stator wedge tightness. One method is to apply steady or impulsive physical force to the stator wedge winding assembly and analyze the resulting deflection. Another method is to apply an excitation signal and analyze the vibratory response. Another method is to measure the profile of the compressed ripple spring in situ and infer the state of compression. Still another method is to install various sensors along the ripple spring that produce signals that may be correlated to the spring's state of compression. Each of these methods for determining the tightness of the wedge requires offline measurements (during which time the generator is not operational) and does not predict the onset of loose wedges. Further, these methods require either time-consuming effort to adjudge the tightness of an individual stator wedge assembly or calibration of a sensor that is proximate to a ripple spring but not an integral part thereof. As the operating environment may reach a continuous temperature in the range −20° C. to 150° C., there is also a need to provide a sensor that will remain stable over the operating temperature regime. Moreover, the accuracies of the sensors often used for monitoring have a tendency to decrease over time.
Therefore, to assess the condition of an electrical machine, there is a need for an efficient monitoring system that more simply and accurately monitors the health of the electrical machine.